What causes rendered frame "flickering"?
It is most likely Z-fighting.
Break down the scene and look if there are any planes in the exact space of orientation.
1 - Could be a hidden object in viewport but still enabled in rendering


2 - Maybe it is an object that is hiding in a different layer.
3 - It could also be 1 object with 2 overlapping faces in the exact same location. (go into edit mode and pull away some edges to check)